Switches are employed in a wide variety of communications systems to route digital signals, such as voice, data, video, and audio signals, from one or more sources to one or more destinations. An N×M multi-port switch may be used to connect any of N input data channels to any of M output data channels. Each of the data channels may be assigned its own physical channel or multiple channels may be multiplexed onto a single physical channel in order to share the physical channel. A strictly non-blocking switch guarantees a connection path will be available between each input channel and each output channel without rearrangement of any existing connections among other ports. A crossbar switch is one example of a strictly non-blocking switch. Some applications, notably synchronous optical network (SONET) systems, require switches to provide, in addition to permutation capability exemplified by non-blocking performance, multi-cast or broadcast capability. That is, switches must feature the ability to switch data from any of the switch's input channels to several or all of its output channels. Providing non-blocking switching capability for large numbers of synchronous transport signals such as level one (STS-1), level three (STS-3), level twelve (STS-12), or other channels within a SONET system can be particularly challenging. SONET and STS-1 are known and discussed, for example, in U.S. Pat. No. 5,715,248 issued to Lagle et al, U.S. Pat. No. 5,781,320 issued to Byers, U.S. Pat. No. 5,742,605 issued to Norman, U.S. Pat. No. 5,383,196 issued to Morton, and U.S. Pat. No. 5,682,257 issued to Uchida, all of which are hereby incorporated by reference.
The number of physical channels (e.g., optical fibers, twisted wire pairs, or coaxial cables) required to carry a group of data channels is often minimized by multiplexing data channels onto a single physical channel, thus avoiding the capital expense associated with installing and maintaining additional physical channels. One consequence of such signal consolidation is the multiplication of data rates on the physical channel. When such high data rate signals are to be switched, the multiplexed data channels may be demultiplexed in order to accommodate the switching speed limitations of the device that is to physically switch data from an input channel to an output channel. For example, a ten-channel, one gigabit per second (Gbs) physical channel could be demultiplexed to ten 100 megabit per second (Mbs) data channels, thereby significantly reducing the switching speed requirements imposed upon the physical switch. There is, therefore, a tradeoff between the number of data channels that may be consolidated on a physical channel and the operating speed required of devices that switch the data channels. Additionally, restrictions on the number of physical input/output connections available to a switch tend to force the consolidation of data channels onto a limited number of physical channels. Restrictions due to input/output limitations are particularly evident at the integrated circuit package level, where designs are sometimes pinout limited. That is, although the specific desired circuit may physically fit within the integrated circuit's (IC's) size limitations, there are not enough input/output pins available accommodate all the signals that must be brought into or taken off of the circuit. Or, the input/output buffers required for that number of inputs and outputs may dissipate too much power. Additionally, the interconnection of various circuit elements on an IC, the interconnection's routing, presents greater difficulties as the complexity of the integrated circuit increases and there tends to be a tradeoff between pinout and size limitations.
In addition to the well known advantages of modular design, such as the reduction of design effort, the re-use of standardized, fully-tested, and therefore reliable modular building blocks, and economies of scale associated with the production of large numbers of modules, modular designs may permit a designer to balance the competing demands of input/output, device size, signal speed, and routing limitations.
A modular switch that accommodates input/output limitations, device switching speed limitations, routing, and device size limitations would therefore be highly desirable.